High-Activity Jobs May Prevent Prostate Cancer

by John Gever John Gever,Staff Writer, MedPage Today
February 13, 2008

Action Points

Explain to interested patients that the study found that aerospace workers whose jobs kept them physically active had lower rates of prostate cancer, after adjusting for chemical exposure and socioeconomic status.

Point out that the study was conducted among workers at a single facility.

Point out that it was a retrospective case-control study that could not control for all factors that may influence cancer risks.

LOS ANGELES, Feb. 13 -- Desk jockeys may be at greater risk for prostate cancer than those whose jobs keep them on the run, researchers here said.

Continual high job activity levels among aerospace workers at a California rocket laboratory were associated with reduced prostate cancer rates (adjusted OR 0.55, 95% CI 0.32 to 0.95) compared with those with the most sedentary jobs, reported Beate Ritz, M.D., Ph.D., M.P.H., of the University of California Los Angeles, and colleagues in the February issue of Cancer Causes & Control.

They stratified the occupations into high-, moderate-, and low-activity levels.

Senior mechanics and technicians, certain inspectors, and engineers were considered moderate-activity occupations.

"The message from this study for today is that if you're more active, you may be able to prevent this cancer from happening. If you have a desk job, do something physically active to counterbalance it," said Dr. Ritz.

The study focused exclusively on activity at work, without regard to recreational exercise.

However, working activity levels made no difference in prostate cancer risk among employees at the same plant who worked on radiation physics projects (adjusted OR 0.95, 95% CI 0.43 to 2.1).

The authors felt that this dissimilarity in the association may be explained by differences in the level of continual versus intermittent physical activity required by their work. Thus, those who worked on radiaton physics projects were likely more highly active on an intermittent, but not daily basis.

The researchers conducted a nested case-control study of 2,167 employees of Rocketdyne, now a subsidiary of Boeing, who worked at the facility from the early 1950s to the early 1990s.

In addition to helping with development of military and NASA rockets, Rocketdyne also was involved with health physics radiation monitoring.

Dr. Ritz and colleagues identified 362 plant workers who were diagnosed with prostate cancer from 1988 through 1999. The researchers compared details of their jobs as well as demographic and medical factors with those of 1,805 Rocketdyne workers matched by age and socioeconomic status who did not develop prostate cancer.

About one-third of the participants worked in radiation monitoring while the rest were employed on the aerospace side.

In calculating the odds ratio for prostate cancer risk, the researchers adjusted for exposure to trichloroethylene and other known or suspected carcinogens and for socioeconomic status.

Among all workers, there was little association between physical activity and prostate cancer, adjusting only for the matching variables (OR for high versus low 0.91, 0.70,

1.2). When also adjusting for trichloroethylene exposure, however, high physical activity level was associated with a decreased risk of prostate cancer.

Dr. Ritz and colleagues used company personnel records and employee interviews to construct a job exposure matrix that quantified activity levels for each employee over their Rocketdyne careers. The matrix also included data on exposures to carcinogenic materials.

The researchers said that cases were more likely than controls to be highly exposed to such chemicals as hydrazine, trichloroethylene, benzene, polycyclic aromatic hydrocarbons, and mineral oil, although they did not give numerical data.

Limitations to their data did not allow Dr. Ritz and colleagues to control for some factors that may affect prostate cancer risk, such as diet and physical activity away from work. The study was also limited to workers at a single facility.

They concluded that "our inability to control for potentially confounding lifestyle factors due to a possible selection bias, however, limits our ability to make causal inference."

The researchers were unable to control fully for race, because Rocketdyne did not systematically record employees' race before 1972. A subgroup analysis of employees whose race was known found an odds ratio of 3.6 among African-American workers for increased prostate cancer risk, although it did not reach significance (95% CI 0.7 to 19) because only seven cancer cases were involved.

Dr. Ritz and colleagues said their findings extend earlier research showing that regular exercise can prevent some forms of cancer, including prostate malignancies.

Information on funding sources or potential conflicts of interest was not reported.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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